feat(ui): add reconcile tick to self-heal lost worker broadcasts

TasksIslandViewModel now runs a periodic tick that diffs the flat Items
collection against SQLite and patches properties in place (capped at 500
rows, sharing the Phase 1 delta sequence guard so it never overtakes a
fresher broadcast). Never rebuilds rows or triggers Regroup/LoadForList, so
it stays decoupled from the parallel Phase 2b virtualization work. The same
cadence now refreshes the long-lived Worktrees Overview, Log Visualizer, and
Merge Helper selection overlays; short-lived modals are untouched.

src/ClaudeDo.Ui/ViewModels/Modals/MergeHelperSelectionModalViewModel.cs

@@ -51,8 +51,18 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
     public TaskCompletionSource<IReadOnlyList<string>?> Result { get; } = new();
     public Action? CloseAction { get; set; }
 
+    private readonly System.Timers.Timer _reconcileTimer = new(4_000);
+
     public MergeHelperSelectionModalViewModel(IDbContextFactory<ClaudeDoDbContext> dbFactory)
-        => _dbFactory = dbFactory;
+    {
+        _dbFactory = dbFactory;
+        // Phase 3 reconcile tick: this overlay is long-lived (stays open while the user ticks
+        // through candidates), so refresh it on the same cadence as TasksIslandViewModel's tick
+        // instead of leaving it frozen at the moment it was opened.
+        _reconcileTimer.Elapsed += (_, _) =>
+            Avalonia.Threading.Dispatcher.UIThread.Post(() => _ = ReconcileTickAsync());
+        _reconcileTimer.Start();
+    }
 
     public void Configure(string listId, string listName)
     {
@@ -60,6 +70,19 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
         ScopeLabel = Loc.T("modals.mergeHelper.scopeList", listName);
     }
 
+    // LoadAsync rebuilds every row from scratch, which would wipe the user's ticks out from
+    // under them on every tick — capture and restore selection by id around the reload.
+    internal async Task ReconcileTickAsync()
+    {
+        if (string.IsNullOrEmpty(_listId)) return;
+        var selected = Tasks.Where(t => t.IsSelected).Select(t => t.Id).ToHashSet();
+        await LoadAsync();
+        foreach (var t in Tasks)
+            if (selected.Contains(t.Id))
+                t.IsSelected = true;
+        OnPropertyChanged(nameof(CanConfirm));
+    }
+
     public async Task LoadAsync(CancellationToken ct = default)
     {
         foreach (var row in Tasks) row.PropertyChanged -= OnRowChanged;
@@ -163,6 +186,7 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
     [RelayCommand]
     private void Confirm()
     {
+        StopReconcileTick();
         Result.TrySetResult(Tasks.Where(t => t.IsSelected).Select(t => t.Id).ToList());
         CloseAction?.Invoke();
     }
@@ -170,7 +194,17 @@ public sealed partial class MergeHelperSelectionModalViewModel : ViewModelBase
     [RelayCommand]
     private void Cancel()
     {
+        StopReconcileTick();
         Result.TrySetResult(null);
         CloseAction?.Invoke();
     }
+
+    // Also called from the dialog's native-close fallback (WindowDialogService), which resolves
+    // Result without going through Confirm/Cancel. Idempotent — Timer.Stop()/Dispose() tolerate
+    // repeated calls.
+    internal void StopReconcileTick()
+    {
+        _reconcileTimer.Stop();
+        _reconcileTimer.Dispose();
+    }
 }